This invention relates to turbochargers and control devices therefor. More specifically, this invention relates to an improved pressure-responsive actuator for controlling the operation of the turbocharger.
Turbochargers are well known in the art, and typically comprise a turbine for driving a compressor to supply relatively high pressure charge air to a combustion engine. The turbine is rotatably driven by exhaust gases from the engine, and in turn rotatably drives a compressor for compressing charge air supplied to the engine. An inherent design problem with turbochargers, however, is that the rotational speed of the turbine and compressor increases as the speed and/or load of the engine increases. At relatively high operating engine speeds or loads, it is possible for the turbine and compressor to be driven at speeds above critical design limits, or for the compressor to supply charge air to the engine at boost pressures higher than the engine can withstand.
A wide variety of control devices for turbochargers have been developed to limit the rotational speed of the turbocharger compressor and thereby to control the boost pressure level of the charge air supplied by the compressor. Such devices can be mounted either on the compressor or the turbine and commonly include blow-off or pop-off valves, turbine bypass or wastegate valves, compressor inlet control valves, and the like. These valve devices are generally similar to each other in principle in that each comprises a valve responsive to a predetermined pressure level or pressure differential to restrict the availability of gases for driving the turbine or for supply to the engine by the compressor. For example, a turbine wastegate valve operates to close a flow path bypassing the turbine and may be opened by a pressure-responsive valve actuator to allow a portion of the engine exhaust gases to bypass the turbine to atmosphere. In this manner, the turbine is rotatably driven by a relatively reduced mass flow of exhaust gases to limit the rotational speed of the turbine and thereby also to limit and control the rotational speed and resultant boost pressure of charge air supplied by the compressor.
Pressure responsive valve actuators typically comprise an actuator housing including a diaphragm which is biased by a relatively stiff spring and which divides the housing into a pair of separate pressure chambers. Inlet ports couple the two pressure chambers to different sources of pressure and/or vacuum to subject the diaphragm to a prescribed pressure differential. Changes in the pressure differential, such as may occur during increases or decreases in engine speed or load, cause displacement of the diaphragm which in turn displaces an actuator rod connected thereto. The rod projects out of the housing, and is connected to an appropriate valve assembly on the turbocharger for positioning a valve to control turbocharger operation.
In practice, one major consideration in the design of pressure-responsive valve actuators is to provide an adequate seal allowing passage of the actuator rod through the actuator housing without significant gas leakage. This is particularly important wherein the pressure sources coupled to the actuator housing comprise gaseous air-fuel mixtures or wherein the actuator housing is mounted in close association to hot engine components or the turbine of the turbocharger. In this regard, prior art seals which have satisfactorily prevented gas leakage typically have restricted displacement of the actuator rod to axial motion only. This type of seal finds its primary application wherein the actuator rod comprises a valve stem connected directly to or formed integrally with a valve head, and wherein axial rod motion is sufficient to properly position the valve head. See, for example, U.S. Pat. Nos. 3,035,408; 3,091,077; 3,104,520; 3,195,805; 3,196,606; 3,270,495; 3,389,553; 4,005,578; 4,005,579; 4,019,323; and 4,075,849, all of which relate to valve actuators with valve stems or rods limited to axial motion. However, it is sometimes desirable to use other types of valve structures, such as a relatively inexpensive butterfly valve or the like positionally adjusted by means of a crank arm. With these alternate valve structures, at least some arcuate motion of the actuator rod is required for adjusting the position of the valve. With prior art devices wherein the actuator rod is constrained for axial movement only, relatively complex and multiple-link mechanical couplings have been required between the rod and the valve structure for accommodating the desired arcuate movement. See for example, U.S. Pat. Nos. 2,356,124; 2,374,708; and 3,096,614.
Some attempts have been made to provide a relatively inexpensive seal for sealing passage of the actuator rod through a turbocharger actuator housing, while at the same time allowing for at least some arcuate actuator rod movement. However, these designs have related to various flexible or elastomeric seal arrangements, or alternately, to the use of seals formed from relatively exotic materials and have not proven totally satisfactory for long life operation in the high temperature vibratory environment of turbochargers. See, for example, copending U.S. Pat. No. 4,251,050 assigned to the same assignee herein. Other designs have proposed the use of spherically-shaped metal sealing members received about the rod and maintained in pivotally sealing engagement with the housing by the relatively stiff spring used for biasing the actuator diaphragm. See, for example, copending U.S. Pat. No. 4,256,019 assigned to the same assignee herein. However, in some applications, the force applied by the stiff spring upon the sealing member is sufficient to prevent free angular displacement of the actuator rod and the sealing member, thereby resulting in binding and undue wear of the components and in relatively slow response to changing pressure differentials.
The present invention overcomes the problems and disadvantages of the prior art by providing an improved turbocharger control actuator having an actuator rod projecting outwardly from an actuator housing and including improved means for sealing passage of the actuator rod through the housing to allow relatively free axial and angular movement of the actuator rod with respect to the housing.